Conventionally, wood scraps, waste paper, used plastics and other waste materials have been simply incinerated in an incinerator for disposal. Because the combustion of waste materials in a normal incinerator is not very efficient, and a large amount of smoke is produced due to insufficient combustion, it has been a common practice to install an auxiliary burner in the passage of smoke for completely burning the smoke.
As an effort to save energy and resources, there has been a desire to develop a boiler which can use the heat produced by burning waste materials for useful purpose. However, the temperature achieved in a normal incinerator is so low as compared to an oil burning boiler that a sufficient amount of heat cannot be recovered from the given amount of waste materials. In other words, the conventional incinerator incorporated with a boiler was so inefficient that the concept of waste burning boiler has never received any wide acceptance.
One solution to this problem is to raise the combustion temperature, and improve the efficiency of heat transfer between the combustion chamber and the water pipes. It is therefore conceivable to install an auxiliary burner inside a main combustion chamber to improve the combustion efficiency and raise the combustion temperature of the main combustion chamber. However, due to increased complexity of the burner structure, and substantial difficulty in adapting the burner to variations in the composition of the fuel consisting of waste materials, this solution cannot produce any satisfactory results.
It has also been proposed to crush the waste materials and form them into solid fuel blocks of a desired size by using a linking agent for the purpose of raising the combustion temperature. However, the cost required for processing the fuel more than offset what might be gained by the use of such a form of fuel. Furthermore, a desired high combustion temperature cannot be obtained without proper burner design, such as installing an auxiliary burner in the main combustion chamber. Thus, practically, this proposal does not offer any satisfactory solution to the problem.